Requires the library mod Collective.

This mod is part of The Vanilla Experience modpack and Serilum's RPG Bundle mod.
Just Mob Heads is a minimalistic mod that adds a configurable chance for mobs to drop their head on death. You can also generate every available mob head via commands. Mob heads will keep their name after placement and pickup with the mod installed.

There are config options available to make mob heads only drop on player kill or only by charged creepers.

I've also got a Just Player Heads mod available!

Contains all four 1.21.9 Copper Golem heads!

Configurable: ( how do I configure? )
The mod allows configuration via two config files. The general one is located in ./config/justmobheads-common.toml and contains:

mobSpecificDropChances (default = true): If enabled, overrides the 'overallDropChance' variable with the specific values.
enableStandardHeads (default = false): If enabled, allows Creepers, Skeletons and Zombies to drop their heads.
enableLootingEnchant (default = true): If enabled, the looting enchant will have an effect on the drop chance.
onlyAdultMobsDropTheirHead (default = true): If enabled, only adult tameable mobs will have a chance to drop their head on death.

overallDropChance (default = 0.1, min 0.0001, max 1.0): Sets the chance of a mob dropping its head if 'mobSpecificDropChances' is disabled.
creeperSkeletonZombieDropChance (default = 0.1, min 0.0001, max 1.0): Sets head drop chance for Zombies, Skeletons and Creepers if 'enableStandardHeads' is enabled.

onlyDropHeadsByChargedCreeper (default = false): When enabled, only drops mob heads if the source on death is a charged creeper. This overwrites the onlyDropHeadsByPlayerKill value.
onlyDropHeadsByPlayerKill (default = false): When enabled, only drops mob heads if the source on death is from a player.

The second config file is located in ./config/justmobheads/headchances.txt. This file contains the default drop chances for all mob head drops (1.19 data):
On first load, the existing values are checked for anything missing (e.g. after an update). If that's the case, it'll be appended to the end of the file.

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"all_black_cat" : 0.5,
"allay" : 0.5,
"armorer" : 0.1,
"bat" : 0.25,
"bee" : 0.1,
"black_and_white_rabbit" : 0.1,
"black_cat" : 0.5,
"black_horse" : 0.1,
"black_rabbit" : 0.1,
"black_sheep" : 0.025,
"blaze" : 0.01,
"blue_axolotl" : 0.5,
"blue_parrot" : 0.75,
"blue_sheep" : 0.025,
"british_shorthair_cat" : 0.5,
"brown_horse" : 0.1,
"brown_llama" : 0.05,
"brown_mooshroom" : 0.05,
"brown_rabbit" : 0.1,
"brown_sheep" : 0.025,
"brown_trader_llama" : 0.25,
"butcher" : 0.1,
"calico_cat" : 0.5,
"cartographer" : 0.1,
"cave_spider" : 0.01,
"charged_creeper" : 1.0,
"chestnut_horse" : 0.1,
"chicken" : 0.05,
"cleric" : 0.1,
"cod" : 0.1,
"cold_frog" : 0.1,
"cow" : 0.05,
"creamy_horse" : 0.1,
"creamy_llama" : 0.05,
"creamy_trader_llama" : 0.25,
"cyan_axolotl" : 0.5,
"cyan_parrot" : 0.75,
"cyan_sheep" : 0.025,
"dark_brown_horse" : 0.1,
"dolphin" : 0.2,
"donkey" : 0.1,
"drowned" : 0.05,
"elder_guardian" : 0.3,
"enderman" : 0.02,
"endermite" : 0.02,
"evoker" : 0.02,
"farmer" : 0.1,
"fisherman" : 0.1,
"fletcher" : 0.1,
"ghast" : 0.1,
"glow_squid" : 0.2,
"goat" : 0.05,
"gold_axolotl" : 0.5,
"gold_rabbit" : 0.1,
"gray_horse" : 0.1,
"gray_llama" : 0.05,
"gray_parrot" : 0.75,
"gray_sheep" : 0.025,
"gray_trader_llama" : 0.25,
"green_parrot" : 0.75,
"green_sheep" : 0.025,
"guardian" : 0.02,
"hoglin" : 0.1,
"husk" : 0.03,
"illusioner" : 0.25,
"iron_golem" : 0.02,
"jeb_sheep" : 0.2,
"jellie_cat" : 0.5,
"killer_rabbit" : 0.1,
"leatherworker" : 0.1,
"librarian" : 0.1,
"light_blue_sheep" : 0.025,
"light_gray_sheep" : 0.025,
"lime_sheep" : 0.025,
"lucy_axolotl" : 0.5,
"magenta_sheep" : 0.025,
"magma_cube" : 0.05,
"mason" : 0.1,
"mooshroom" : 0.05,
"mule" : 0.1,
"nitwit" : 0.1,
"ocelot" : 0.1,
"orange_sheep" : 0.025,
"panda" : 0.5,
"persian_cat" : 0.5,
"phantom" : 0.1,
"pig" : 0.05,
"piglin" : 0.05,
"piglin_brute" : 0.1,
"pillager" : 0.2,
"pink_sheep" : 0.025,
"polar_bear" : 0.2,
"pufferfish" : 0.1,
"purple_sheep" : 0.025,
"ragdoll_cat" : 0.5,
"ravager" : 0.2,
"red_cat" : 0.5,
"red_fox" : 0.25,
"red_parrot" : 0.75,
"red_sheep" : 0.025,
"salmon" : 0.1,
"salt_and_pepper_rabbit" : 0.1,
"shepherd" : 0.1,
"shulker" : 0.05,
"siamese_cat" : 0.5,
"silverfish" : 0.05,
"skeleton_horse" : 0.25,
"slime" : 0.05,
"snow_fox" : 0.25,
"snow_golem" : 0.1,
"snowman" : 0.05,
"spider" : 0.05,
"squid" : 0.05,
"stray" : 0.1,
"strider" : 0.1,
"tabby_cat" : 0.5,
"tadpole" : 0.05,
"temperate_frog" : 0.1,
"toast_rabbit" : 0.5,
"toolsmith" : 0.1,
"tropical_fish" : 0.1,
"turtle" : 0.1,
"vex" : 0.25,
"villager" : 0.1,
"vindicator" : 0.25,
"wandering_trader" : 1.0,
"warden" : 1.0,
"warm_frog" : 0.1,
"weaponsmith" : 0.1,
"white_cat" : 0.5,
"white_horse" : 0.1,
"white_llama" : 0.05,
"white_rabbit" : 0.1,
"white_sheep" : 0.025,
"white_trader_llama" : 0.25,
"wild_axolotl" : 0.5,
"witch" : 0.05,
"wither" : 1.0,
"wolf" : 0.05,
"yellow_sheep" : 0.025,
"zoglin" : 0.1,
"zombie_armorer" : 0.1,
"zombie_butcher" : 0.1,
"zombie_cartographer" : 0.1,
"zombie_cleric" : 0.1,
"zombie_farmer" : 0.1,
"zombie_fisherman" : 0.1,
"zombie_fletcher" : 0.1,
"zombie_horse" : 0.25,
"zombie_leatherworker" : 0.1,
"zombie_librarian" : 0.1,
"zombie_mason" : 0.1,
"zombie_nitwit" : 0.1,
"zombie_shepherd" : 0.1,
"zombie_toolsmith" : 0.1,
"zombie_villager" : 0.1,
"zombie_weaponsmith" : 0.1,
"zombified_piglin" : 0.1,

Commands
/jmh reload - Reloads all changes made to the "./config/justmobheads/headchances.txt" config file.
/jmh head list - Lists all mobnames of available mob heads.
/jmh head <mobname> <amount> - Generates <amount> of heads from <mobname>.

Command examples:

Show Spoiler

Texture values instead of generation via player-names
The mod uses texture values to generate the mob heads. This means that there won't be any lag, which player-name generated heads usually cause.

Pure Vanilla Resources
Because the mod does not add any custom blocks, you may remove the mod and still have the heads previously gathered in-game.

When does a head drop?
Whenever the player kills a mob, there is a chance that they drop their head. There are pre-defined chances in the config file, but you may alter them to your liking. It'll be dropped at their death location.

How many mobs are added?
Every mob has been added. When Minecraft updates, the newly added mobs receive a head drop as well. You can see the entire mob head list above under configurable.

What about Creepers, Skeletons and Zombies?
By default the standard heads do not drop, because you can collect them via a charged creeper. You can however enable the option within the config file for all three to drop their respective head on death just as any other mob.

Does Looting have an effect?
The Looting enchant has an effect on the head drop chance. This can be enabled/disabled within the config file. The increased chance is 3.5% at level I, 4.5% at level II, and 5.5% at level III and so forth. It also works with looting levels higher than 3.

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You may freely use this mod in any modpack, as long as the download remains hosted within the Modrinth ecosystem.

Serilum.com contains an overview and more information on all mods available.

Comments are disabled as I'm unable to keep track of all the separate pages on each mod.
For issues, ideas, suggestions or anything else there is the Github repo. Thanks!

Considerations

CTM Optifine - Fabric